Nobody has adopted Prefetch yet. Adopt a bot: you get one at random, and your name goes on its plaque. It might be this one.
Identification
Its full user-agent string, exactly as it arrives at the gate:
There is no operator to verify against. This name is what software calls itself when nobody gave it one.
No operator stands behind this name, so there is nothing to check its visits against.
How to block Prefetch
Add these two lines to the robots.txt file at the root of your site. Well-behaved crawlers read it before they crawl, so the change applies from Prefetch's next visit. Nothing else on your site needs to change.
# Block Prefetch from the whole site User-agent: Prefetch Disallow: /
Or let it visit but keep it away from part of the site:
# Let it in, but keep it out of one room User-agent: Prefetch Allow: / Disallow: /members/
Observed behaviour
Most active around 00:00. The keepers are asleep. It knows.
Requested 0 disallowed pages out of 24 requests. Never read robots.txt.
Has never followed the hidden link to /trap/. Either well trained or very lucky.
Where it comes from
Scripts and scanners run from wherever their owners rent a server. These are the networks behind the visits on file:
Networks and countries come from the visitor's IP address, looked up in a local copy of the DB-IP database. The addresses themselves are never stored.
Keeper's field notes
Questions site owners ask
Does Prefetch respect robots.txt?
We can't say yet. It has not fetched robots.txt here, and it has not touched a disallowed page either.
Will blocking Prefetch hurt my search rankings?
No. Nothing respectable will miss it.
How often does Prefetch visit?
Here, about 3 requests a day over the last week. Visits to your site depend on its size, how often it changes, and how many links point to it.